    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one or more
    003 * contributor license agreements.  See the NOTICE file distributed with
    004 * this work for additional information regarding copyright ownership.
    005 * The ASF licenses this file to You under the Apache License, Version 2.0
    006 * (the "License"); you may not use this file except in compliance with
    007 * the License.  You may obtain a copy of the License at
    008 *
    009 *     http://www.apache.org/licenses/LICENSE-2.0
    010 *
    011 * Unless required by applicable law or agreed to in writing, software
    012 * distributed under the License is distributed on an "AS IS" BASIS,
    013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014 * See the License for the specific language governing permissions and
    015 * limitations under the License.
    016 */
    017package org.apache.commons.configuration2.tree;
    018
    019import java.util.List;
    020import java.util.Set;
    021
    022/**
    023 * <p>
    024 * Definition of an interface for accessing the data of a configuration node.
    025 * </p>
    026 * <p>
    027 * Hierarchical configurations can deal with arbitrary node structures. In order
    028 * to obtain information about a specific node object, a so-called
    029 * {@code NodeHandler} is used. The handler provides a number of methods for
    030 * querying the internal state of a node in a read-only way.
    031 * </p>
    032 *
    033 * @version $Id: NodeHandler.java 1636033 2014-11-01 20:47:47Z oheger $
    034 * @param <T> the type of the nodes this handler deals with
    035 */
    036public interface NodeHandler<T>
    037{
    038    /**
    039     * Returns the name of the specified node
    040     *
    041     * @param node the node
    042     * @return the name of this node
    043     */
    044    String nodeName(T node);
    045
    046    /**
    047     * Returns the value of the specified node.
    048     *
    049     * @param node the node
    050     * @return the value of this node
    051     */
    052    Object getValue(T node);
    053
    054    /**
    055     * Returns the parent of the specified node.
    056     *
    057     * @param node the node
    058     * @return the parent node
    059     */
    060    T getParent(T node);
    061
    062    /**
    063     * Returns an unmodifiable list with all children of the specified node.
    064     *
    065     * @param node the node
    066     * @return a list with the child nodes of this node
    067     */
    068    List<T> getChildren(T node);
    069
    070    /**
    071     * Returns an unmodifiable list of all children of the specified node with
    072     * the given name.
    073     *
    074     * @param node the node
    075     * @param name the name of the desired child nodes
    076     * @return a list with all children with the given name
    077     */
    078    List<T> getChildren(T node, String name);
    079
    080    /**
    081     * Returns an unmodifiable list of all children of the specified node which
    082     * are matched by the passed in {@code NodeMatcher} against the provided
    083     * criterion. This method allows for advanced queries on a node's children.
    084     *
    085     * @param node the node
    086     * @param matcher the {@code NodeMatcher} defining filter criteria
    087     * @param criterion the criterion to be matched against; this object is
    088     *        passed to the {@code NodeMatcher}
    089     * @param <C> the type of the criterion
    090     * @return a list with all children matched by the matcher
    091     */
    092    <C> List<T> getMatchingChildren(T node, NodeMatcher<C> matcher, C criterion);
    093
    094    /**
    095     * Returns the child with the given index of the specified node.
    096     *
    097     * @param node the node
    098     * @param index the index (0-based)
    099     * @return the child with the given index
    100     */
    101    T getChild(T node, int index);
    102
    103    /**
    104     * Returns the index of the given child node in the list of children of its
    105     * parent. This method is the opposite operation of
    106     * {@link #getChild(Object, int)}. This method returns 0 if the given node
    107     * is the first child node with this name, 1 for the second child node and
    108     * so on. If the node has no parent node or if it is an attribute, -1 is
    109     * returned.
    110     *
    111     * @param parent the parent node
    112     * @param child a child node whose index is to be retrieved
    113     * @return the index of this child node
    114     */
    115    int indexOfChild(T parent, T child);
    116
    117    /**
    118     * Returns the number of children of the specified node with the given name.
    119     * This method exists for performance reasons: for some node implementations
    120     * it may be by far more efficient to count the children than to query a
    121     * list of all children and determine its size. A concrete implementation
    122     * can choose the most efficient way to determine the number of children. If
    123     * a child name is passed in, only the children with this name are taken
    124     * into account. If the name <b>null</b> is passed, the total number of
    125     * children must be returned.
    126     *
    127     * @param node the node
    128     * @param name the name of the children in question (can be <b>null</b> for
    129     *        all children)
    130     * @return the number of the selected children
    131     */
    132    int getChildrenCount(T node, String name);
    133
    134    /**
    135     * Returns the number of children of the specified node which are matched by
    136     * the given {@code NodeMatcher}. This is a more generic version of
    137     * {@link #getChildrenCount(Object, String)}. It allows checking for
    138     * arbitrary filter conditions.
    139     *
    140     * @param node the node
    141     * @param matcher the {@code NodeMatcher}
    142     * @param criterion the criterion to be passed to the {@code NodeMatcher}
    143     * @param <C> the type of the criterion
    144     * @return the number of matched children
    145     */
    146    <C> int getMatchingChildrenCount(T node, NodeMatcher<C> matcher, C criterion);
    147
    148    /**
    149     * Returns an unmodifiable set with the names of all attributes of the
    150     * specified node.
    151     *
    152     * @param node the node
    153     * @return a set with the names of all attributes of this node
    154     */
    155    Set<String> getAttributes(T node);
    156
    157    /**
    158     * Returns a flag whether the passed in node has any attributes.
    159     *
    160     * @param node the node
    161     * @return a flag whether this node has any attributes
    162     */
    163    boolean hasAttributes(T node);
    164
    165    /**
    166     * Returns the value of the specified attribute from the given node. If a
    167     * concrete {@code NodeHandler} supports attributes with multiple values,
    168     * result might be a collection.
    169     *
    170     * @param node the node
    171     * @param name the name of the attribute
    172     * @return the value of this attribute
    173     */
    174    Object getAttributeValue(T node, String name);
    175
    176    /**
    177     * Checks whether the specified node is defined. Nodes are
    178     * &quot;defined&quot; if they contain any data, e.g. a value, or
    179     * attributes, or defined children.
    180     *
    181     * @param node the node to test
    182     * @return a flag whether the passed in node is defined
    183     */
    184    boolean isDefined(T node);
    185
    186    /**
    187     * Returns the root node of the underlying hierarchy.
    188     *
    189     * @return the current root node
    190     */
    191    T getRootNode();
    192}